What is Pn junction: Definition and 92 Discussions

A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains an excess of electrons in the outer shells of the electrically neutral atoms there. This allows electrical current to pass through the junction only in one direction. The p-n junction is created by doping, for example by ion implantation, diffusion of dopants, or by epitaxy (growing a layer of crystal doped with one type of dopant on top of a layer of crystal doped with another type of dopant). If two separate pieces of material were used, this would introduce a grain boundary between the semiconductors that would severely inhibit its utility by scattering the electrons and holes.p–n junctions are elementary "building blocks" of semiconductor electronic devices such as diodes, transistors, solar cells, LEDs, and integrated circuits; they are the active sites where the electronic action of the device takes place. For example, a common type of transistor, the bipolar junction transistor, consists of two p–n junctions in series, in the form n–p–n or p–n–p; while a diode can be made from a single p-n junction. A Schottky junction is a special case of a p–n junction, where metal serves the role of the n-type semiconductor.

View More On Wikipedia.org
  1. E

    I have a question about diodes and the PN junction

    Is the PN junction inside a diode what makes the electrical current only flow in one direction and not in the opposite direction? If this is so, why does it happen? Also Why is the P-type material said to have empty holes and the N-type material to have free electrons?
  2. E

    I How does diffusion of high energy electrons shift band structure?

    When an n-type material comes in contact with a p-type material to form pn-junction, electrons with the highest energy in the conduction band will diffuse to the p-side to reach equilibrium so the entire band structure on n-side will shift down relative to p-side as described in the following...
  3. Mayan Fung

    I Measuring the built-in potential of a pn junction

    I am thinking about the reason why we cannot probe the built-in potential across a diode with a voltmeter. Obviously, a diode is not an energy source, so it is impossible for it to show a voltage reading. After doing some research, I found some explanations and some questions about them. 1. The...
  4. Stonestreecty

    Help with the Key Points of Zener Breakdown and Avalanche Breakdown

    Good day, all I am familiar with both of terms that I speak of in title. But I cannot find a full answer, so I might as well ask the PhD'ers here. What is really happening in Zener and Avalanche breakdown? I have read Guide to Zener Effect and Avalanche Effect and still feel confused. And yes I...
  5. Mr_Allod

    Calculating the speed of a JFET

    Hello there, I believe here I need to find the capacitance of the junction between the P-doped gate and N-channel. Then I could find the RC time constant although I am not sure if there's something more I need to find the speed of the JFET? What I'm unsure of is the depletion width h to use...
  6. Mr_Allod

    Built in Voltage of 3-Layer PN Junction

    For a normal PN junction I would try to find $V_{bi}$ by integrating the carrier density (eg. the electrons n) from one region to the other: $$\int_{n_{p0}}^{n} \frac {dn}{n} = \frac {q}{kT}\int_{V_p}^{V_n} dV$$ Which would yield: $$V_{bi}=V_n-V_p=\frac...
  7. Mr_Allod

    Depletion width of linearly doped PN-junction

    Hello there, I have derived the expressions for electric field and potential to be the ones above, then for continuity at ##x = 0## I set the electric fields and potentials to be equal to yield the expressions: $$Sx_p^2 = Kx_n^2$$ $$V_{bi} = V_n - V_p = \frac {q}{3\epsilon} \left( Sx_p^3 +...
  8. U

    PN Junction at Equilibrium

    Consider a PN junction doped with say phosphorous on the N side, and Boron on the P side. Initially, there is an opportunity for the electrons just below the N conduction band to drop to the lower available energy states just above the P valence band. This leaves the N side positively charged...
  9. Kaushik

    B How does the doping concentration affect the depletion width?

    I do not understand why that is the case. Is there any intuitive explanation for it? Thanks
  10. T

    Fundamentals of the PN Junction

    Unbiased circuit (no driving voltage source) ************** Fig 1 The N-type material has a tendency to donate electrons to the P-type (i.e. absorb holes from) across the PN junction via diffusion current exclusively within the conduction band of both materials. It does so after those...
  11. Praveen1901

    B P-N junction Semiconductors

    I'm new to semiconductors. While I was studying types of biasing in semiconductors, here's what I read - 'In forward biasing, the width of the depletion region is reduced.' Here's what I thought - Since the potential barrier is reduced in the junction due to external potential, the diffusion...
  12. Muhammad Usman

    I Physics behind P-N Junctions?

    I was reading the PN junction. During the formation of PN junction diffusion process takes place in which the free electrons cross the boundary of the P-N and joined with the holes in the P-type to form the negative ion and holes on the N side cause positive ions. So, the P-side has negative...
  13. T

    Pn junction under forward bias

    If two batteries are connected such that positive terminal of one is in contact with negative terminal of other then we add the potentials so the potential will then be their sum. Similarly if a battery is connected to a pn junction diode such that positive terminal is connected to negative...
  14. Wrichik Basu

    Do carriers move across a p-n junction at 0 K?

    Often a band diagram is used to explain what happens when two pieces of the same semiconductor, one p-doped, one n-doped, are put together. I am a little confused about it, so here is my question. Initially and at ##0\mathrm{K}##, the surplus carriers should be confined to their respective...
  15. G

    I Relationship between the depletion region and the band gap of a diode?

    Hi, Lately I've been reading about a lab exercise in which Planck's constant is estimated using LEDs. Every procedure I've encountered states that the energy of an emitted photon (and by extension the potential across the semiconductor's band gap) is equal to the threshold voltage multiplied by...
  16. E

    I Concentration of R-G centers in a PN junction

    Hey guys, Currently taking a semiconductor device fundamentals course and we are learning about R-G currents in the depletion region of a PN junction. Usually we just consider R-G centers as impurities to be avoided in the operation of a standard rectifying diode. However, I was curious as to...
  17. T

    B Forward Bias: Why does width of depletion layer decrease?

    The depletion layer is formed by the movement of electrons from the n to p side and holes from p to n side of the diode. The layer consists of positively charged donor ions close to the n side and negatively charged acceptor ions close to the p side. When in equilibrium,the barrier potential...
  18. C

    PN Junction Depletion Layer

    Homework Statement I'm doing a course in solid state electronics and we just started PN junctions etc. I'm a bit confused. So here is what I know so far: Initially the P and N regions are separated by a a PN junction. At 300K as the acceptor atoms on the P side and donor atoms on the N side...
  19. D

    I Exploring PN Junction Loop: Fermi Level and Work Function

    Hi. So we have all seen the band diagram of a PN junction. In order for the fermi level to be the same on both sides, the P bands are shifted up or the N bands are shifted down. Now that the fermi levels are equal, what would happen if you bent the diode into a ring (annulus) shape? How would...
  20. Dr. Manoj

    PN Junction Diode: Diffusion vs. Drift Current

    What exactly is difference between diffusion current and drift current?
  21. Dr. Manoj

    Zener Diode Breakdown: Effects on PN Junction & Holes/Electrons

    Once the zener Diode is formed by breakdown of pn junction Diode, potential across Diode remains constant. If we again change the configurations from reverse bias to forward bias, is it possible to get back the normal pn junction as before the breakdown and will potential across junction be...
  22. D

    I PN Junction Current: Understanding Dependence on Parameters

    Hi. I'm trying to understand how the current in a PN junction depends on various parameters. I have found this formula in Ashcroft and Mermin. It looks like the current will increase if we decrease the density of donors and/or acceptors, Na and Nd. Is this correct?
  23. E

    I Double heterostructure junction in forward and zero bias

    Hi! When dealing with a pn homojunction, it is easy to see the features it has at equilibrium, and also the features it has with forward/reverse bias. Plots show the constant Fermi level at equilibrium and the different Fermi levels for a forward bias; moreover, examples show how much the bands...
  24. E

    I Built-in potential in pn junction

    Hello! The (potential) energy of an electron in a solid structure is always negative; also the E_c and E_v levels (conduction band and valence band limits) are negative, in the band diagram of a pn junction. When the junction is built and thermal equilibrium is reached, the depletion region...
  25. E

    I Diffusion of carriers in a double heterostructure

    Hello! Double heterostructures are used in LEDs and lasers to provide both the confinement of the charge carriers and the confinement of the generated light. This image is a comparison between a homojunction and a heterojunction. As regards the unbiased junctions, when the n region and the p...
  26. E

    I Pn junction to reach thermal equilibrium

    Hello! Some of the processes caused by a pn junction are not clear for me. Just after the contact between the p and the n region, a migration of charges happens in a semiconductor junction in order to reach an equilibrium condition. A valence band and a conduction band are present in both...
  27. G

    Depletion zone and current in forward-biased PN junction

    Hello. I've learned that in PN junction, forward-biasing on it pushes holes in P-type and electrons in N-type toward the junction so depletion width is reduced. Is it due to that in N-type side(P-type side), pushed electrons (holes) are recombined with holes (electrons) in depletion zone? And...
  28. G

    Depletion zone and current in forward-biased PN junction

    Hello. I've learned that in PN junction, forward-biasing pushes holes in P-type and electrons in N-type forward junctions so depletion width is reduced. Is it due to that in N-type (P-type), pushed electrons (holes) are recombined with holes (electrons) in depletion zone? And what is true...
  29. D

    Question about pn diodes and their lifetime

    I was wondering, does the lifetime of a diode depend on how long it takes for all the free P electrons to transfer over to the p holes? In other words, do the electrons that fall into the p holes ever return to the n side?
  30. A

    Short circuited illuminated PN junction

    I understand why the potential difference across the pn junction decrease in case of the open circuit, but why does it decrease in the short circuit, And why in the J-V equation we use V = Voc ( where qVoc is the energy between the quasi fermi levels) and what if the quasi fermi levels aren't...
  31. Corwin_S

    Maximum Built-In Voltage of a PN junction

    Hi, I'm familiar with the expression for calculating the built-in voltage of a p-n junction. How can I find the maximum built-in voltage before the semiconductor becomes degenerate (i.e., a bad metal) if I only know the material and the intrinsic carrier concentration at a given temperature...
  32. cnh1995

    Built-in voltage of pn junction diode

    Why can't the built-in voltage of diode be measured by a voltmeter when the diode is isolated? A potential difference of almost 0.7V exists at the junction, which is clearly not too small for the voltmeter to detect. What's the reason?
  33. N

    From where we measure current in a pn junction diode

    Please anyone explain me from where we measure current or we apply ammeter in a pn junction diode to measure current
  34. Amal Thejus

    Static or Dynamic equlibrium in a PN junction?

    Homework Statement We are considering an UNBIASED junction.[/B] I've read in a textbook that electric field created in the junction STOPS diffusion BUT in the same text its written the drift and diffusion currents cancel each other. 1. Does the diffusion and drift currents occur simulataneously...
  35. Amal Thejus

    How can the neutral regions in a diode have constant potential?

    Homework Statement It is said that the potential in the neutral regions of a PN junction diode is CONSTANT. Homework Equations V=Q/4ΠΣr The Attempt at a Solution It is said in all textbooks to ASSUME that the electric field in the neutral regions as zero. Two aspects confuse me. 1. What...
  36. Amal Thejus

    ACTUAL Variation of Potential inside a diode.

    Homework Statement The figures showing the potential variation inside a PN junction normally shows the potential to be constant in the neutral P and N regions Homework Equations V=Q/4ΠΣr The Attempt at a Solution Since the potential due to the positive and negative charges should also exist...
  37. P

    PN Junction: Current flow in Reverse Bias

    Can someone explain why after a certain voltage, current flows. We were taught that in pn junction when a reverse voltage is applied the depletion region grows wider. Using this no matter what the voltage current should not increase. So why does a current flow when a reverse current is applied.
  38. Amal Thejus

    Why there is NO current in a PN junction under equilibrium

    Homework Statement Its said that there is no Net current in a PN junction under equilibrium as the drift and diffusion currents cancel each other. We are talking about a Step junction at equilibrium. Homework Equations Its just a qualitative analysis. 3. The Attempt at a Solution [/B] The...
  39. Amal Thejus

    Variation of Potential outside a PN junction

    Homework Statement 1. We are considering a step junction at equilibrium(no external voltage applied). 2. The potential variation is shown as negative potential at P region(which is shown as constant) and increasing through the transient region to become positive in the n region. Homework...
  40. Amal Thejus

    Variation of Potential outside the PN junction

    Homework Statement 1. We are considering a step junction at equilibrium(no external voltage applied). 2. The potential variation is shown as negative potential at P region(which is shown as constant) and increasing through the transient region to become positive in the n region. Homework...
  41. D

    Does any current flow in reverse PN junction?

    Homework Statement Homework Equations [/B] When a diode is reverse biased positive donor ions are left in the N semiconductor and negative acceptor ions in the P type. And since the N is conected to + and its donnor ions has a large +charge, why no electrons from P cannot cross the junction...
  42. D

    Reverse biased pn junction

    [Mentor's Note: Thread moved and edited by mentor.] Sorry I am new and I had problems creating the thread. But I will post my question here:-D. So in reverse biased pn junction the width of the depletion layer increases. But on the N side a large positive charge from the donnor ions is...
  43. G

    Drift current of a PN junction

    The magnitude of a drift current density is given by J = qnv, where q is the carrier charge, n is the carrier density per unit volume, and v is the carrier drift velocity. q is a physical constant and n is independent of bias. But when an external electric field is applied, the minority charge...
  44. H

    Is E-field in pn-junctions changing linearly with bias?

    Hi guys, there are a lot of textbooks and articles describe the electric field in depletion region at thermal equilibium, but very few of them tell what happens to the field under bias. I am wondering if the electric field in the depletion region simply changes linearly with reverse bias? Or if...
  45. O

    What is the polarity of a Pn junction diode

    Hello all Textbooks teaches us that in the formation of Pn junction in between P and N type semiconductor a region is formed where free electrons of N diffused in P side and exhaust by the holes of P near the junction. Such a region becomes devoit of free charge careers and their are only ions...
  46. CKaiL

    PN Junction Q&A: Reverse Bias Voltage at Cathode

    Homework Statement [PLAIN]http:// Homework Equations The Attempt at a Solution It has becomes a P type semi conductor due to the fact that there is more acceptor than donor. From definition , forward bias is the direction of easy current flow while reverse bias is in the direction of...
  47. N

    Pn junction diode (series combo of voltage source and diode)

    The question is to solve the current through a resistor after a pn junction. (photo attached) As far as I'm aware the voltage source in the pn junction is (in this orientation) of opposite polarity to that of the 0.8V voltage source. From my understanding the answer goes like: V=IR I=V/R...
  48. A

    Law of the PN junction under forward bias. Valid ?

    I'm currently studying the physics of the PN junction. I went though the derivation of the built-in potential in the PN junction under equilibrium: Diffusion current density = Drift current density D_{p}p\frac{dp}{dx} = EU_ppq where D_{p} : Diffusion coefficient for holes p = holes density...
  49. G

    PN Junction. Silicon vs Germanium

    When we connect P and N materials, electrons from N drift to P, thus create negative ions in P and positive ions in N. => electric field (barrier potential) must depend on an amount of electrons recombined with holes in P region. => The more electrons recombined, the more ions created, the...
  50. M

    Understand PN Junction Diode: Diffusion & Electrons

    If p-type semiconductor and n-type semiconductor of a diode are equally doped, and if the diode is forward biased, then holes will move toward the n-type semiconductor and electrons will move toward the p-type semiconductor and they will diffuse with each other and the ions become neutral atoms...